Substance use disorders (SUDs) are a highly prevalent and often untreated problem for incarcerated individuals in the United States, and they are associated with eventual relapse, recidivism, and repeated incarceration. Although SUDs are clearly linked to negative outcomes post-release, the vast majority of inmates do not have access to treatment during their incarceration. Complicating the clinical picture, incarcerated substance users also suffer from higher rates of co-occurring depression and other psychopathology. Inmates with these co-occurring disorders are at even higher risk of multiple incarcerations, and require a more integrated treatment approach. Behavioral Activation (BA) may be well equipped to address the unique needs of this population. It is an efficient, straightforward, and cost-effective treatment that has been adapted for a variety of settings and populations, including a group version called LETS ACT designed for depressed low-income substance users. This approach, however, has yet to be tested with substance users in a correctional setting. The current study will compare LETS ACT to treatment as usual in longitudinal outcomes of substance use, depression, and objective measures such as probation violations, arrests, and future incarceration among incarcerated substance users. It is hypothesized that LETS ACT will be associated with a decrease in depression at the conclusion of treatment, and reductions in all other outcomes in the year following release with particular attention to substance use relapse and recidivism. The work proposed in this application will provide a much-needed test of a targeted intervention for this at risk population. Moreover, this research will provide important data on LETS ACT's efficacy in a correctional environment, and if successful, will set the stage for future work in disseminating the intervention. The main training goal for this project is to develop a line of research to better understand and treat factors related to repeated criminal justice involvement among incarcerated substance users and ultimately impact society through limiting substance use and repeated incarceration.